Promoters water

Magnesium is not attacked seriously by dry chlorine [7782-50-5] iodine [7553-56-2] bromine, or fluorine [7782-41 ] gas. However, the presence of water promotes attack. Similarly, sulfur dioxide, ammonia, and fluorine-containing refrigerants do not attack in the absence of water. 

Zavitsas et al. account for the effects of water in their calculations. Water promotes depolymerization of the paraformaldehyde as well as the hemiformals. Their modifications correct for the apparent reduction in methylolation rate as the extent of reaction proceeds, in that the hemiformals remove formaldehyde reactivity from the reaction mixture. Their rate constants look large because they are written for phenate concentrations rather than phenol and because of the formaldehyde equilibrium adjustments. They note that unsalted phenol is a by-... 

Solar beating of tropical oceans warms the surface water, promoting evaporation. Where the equatorial surface waters are warmest and the northeast and southeast trade winds meet, a band of cirrostratus and cirrus clouds spreads out from convective precipitation regions. This area is known as the Intertropical Convergence Zone. 

Effect of Solvent and Base on the Ruthenium Carbonyl/Tri-methylamine System. Solvent plays an important role in the rate of hydrogen production. The ideal solvents are tetrahydrofuran, diglyme, and dimethoxyethane. Alcohols are only slightly less effective. Apparently the solvent must be miscible with water, promote ion formation, and be capable of weakly coordinating with the coordinately unsaturated species formed in the course of the reaction. 

Lewis-acid catalysis (Table 7.2) was observed for Cu, Ni " , Co, and Zn " ", with Cu being the best catalyst (both strongest binding and most efficient in accelerating the reaction with CPD). Varying the solvent (Table 7.3) in the catalysis by Cu ions with L-abrine as a ligand illustrates a large increase in enantioselectivity in water. So water promotes enantioselectivity. ... 

Figure 1.11 provides an example of H NMR monitoring in the Pd-catalyzed cy-doisomerization of dimethyl diallyl malonate, 39 [28]. The kinetic profile reveals a pronounced induction period after which the exocydic alkene 40a is formed predominantly as the kinetic product. A hydropalladation mechanism was proposed on the basis of NMR experiments, and the transient spedes 41, formed by allylpalla-dation of the coordinated diene, could be detected and identified with the help of and labeling. The hydride Pd catalyst, 42, would be generated from 41 by water-promoted P-hydride elimination. The observed induction period is assodated with the formation of the Pd-hydride 42. 

Water has also been shown to be essential for the liquid phase polymerization of isobutylene with stannic chloride as catalyst (Norrish and Russell, 87). The rates of reaction were measured by a dilatometric method using ethyl chloride as common solvent at —78.5°. With a mixture consisting of 1.15% stannic chloride, 20 % isobutylene, and 78.8% ethyl chloride, the rate of polymerization was directly proportional to the amount of added water (up to 0.43% of which was added). A rapid increase in the rate of polymerization occurred as the stannic chloride concentration was increased from 0.1 to 1.25% with higher concentrations the rate increased only gradually. It was concluded that a soluble hydrate is formed and functions as the active catalyst. The minimum concentration of stannic chloride below which no polymerization occurred was somewhat less than half the percentage of added water. When the concentration of the metal chloride was less than about one-fifth that of the added water, a light solid precipitated formation of this insoluble hydrate which had no catalytic activity probably explains the minimum catalyst concentration. The addition of 0.3% each of ethyl alcohol, butyl alcohol, diethyl ether, or acetone in the presence of 0.18% water reduced the rate to less than one-fifth of its normal value. On the other hand, no polymerization occurred on the addition of 0.3 % of these substances in the absence of added water. The water-promoted reaction was halved when 1- and 2-butene were present in concentrations of 2 and 6%, respectively. 

Adsorbed water promotes self adhesion of Fe oxide particles in powders (e. g. cosmetics) which can lead to problems with clumping (Tsugita et al., 1990). 

Water treatment by either direct or contact filtration has become common practice for raw water with low turbidity [<3NTU] and low colour. Simple metal salts such as alum or ferric chloride are added to plant inlet water. Hydrolysis takes place with the formation of hydroxylated species, which adsorb, reducing or neutralizing the charge on the colloidal particles in the raw water, promoting their collision and the formation of floes that settle or can be filtered out. 

Organic Reactions in Micro-Organized Media—Why and How Water-Promoted Organic Reactions The design of green oxidants Water as a solvent for chemical reactions Water as a benign solvent for chemical syntheses... 

The treatment of gout involves diet and medication. The diet should be low in protein (so as to reduce acidity), provide adequate water, promote weight control, and includes no alcohol. Various antiinflammatory drugs can be prescribed but those which are acids such as aspirin will worsen the situation. 

When cone, sulphuric acid acts on the alcohols, the acid esters only are formed, though sulphuric acid, by its great affinity for water, promotes almost complete esterification in other instances for the preparation of normal sulphuric esters, see Preparation 210. 

Lubineau, A., Auge, J. and Queneau, Y., Water-promoted organic reactions, Synthesis, 1994, 741. 

Interestingly, water promotes a non-radiative decay of [Ru(bipy)3]2+. It seems reasonable that within the Nafion film the ruthenium(II) species minimizes its contact with water,49 which helps to explain the ability of the film to retain relatively hydrophobic counter ions. The more hydrophilic [Ru(bipy)3]3+ is in fact more labile from the film than the bipositive complex.44... 

The second QSAR is for water-promoted dehyrobromination and also is based on Cj but is much more sensitive to inductive effects of other substitutents (X.o,), as equations (28) and (29) show ... 

The water-promoted hydrolyses of a bicyclic amide, l-azabicyclo[2.2.2]octan-2-one (87), and a planar analogue, l,4-dimethylpiperidin-2-one (88), were studied using density functional theory in conjunction with a continuum dielectric method to introduce bulk solvent effects. The aim of these studies was to reveal how the twisting of the C-N bond affects the neutral hydrolysis of amides. The results predict important rate accelerations of the neutral hydrolysis of amides when the C-N bond is highly twisted, the corresponding barrier relaxation depending on the specific reaction pathway and transition state involved.85... 

The diastereoselective halohydrin formation, resulting from the reaction of chiral /V -enoyI -2-oxazoI idinones with Br2/l2 and water, promoted in the presence of silver , in aqueous organic solvents, has been found to occur with high regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl, and electron-deficient cinnamoyl substrates readily produced the bromohydrin in aqueous acetone, but no iodohydrin formation was observed under these conditions. On the other hand, ( ) electron-rich cinnamoyl substrates preferred to afford iodohydrins in aqueous acetone with moderate diastereoselectivity enhanced diastereoselectivity was observed for aqueous THF.31... 

Treatment of symmetrically substituted bis(arylmethylthio)alkynes with either IC1 or Br2 and in the strict absence of water promotes cyclization to 1//-2-benzothiopyrans (Scheme 129). Initial formation of a cyclic halonium species induces the electrophilic ring closure. In the presence of nucleophiles, ipso attack is favored and a spirocyclohexa-dienone results. The alkynes are accessible from arylmethyl thiocyanates and sodium acetylide <1998JOC4626, 2003EJ047>. 

The presence of significant quantities of physisorbed water promotes the chemisorption of alkoxysilanes, especially of the ones with two or three alkoxy groups. Engelhardt and Orth90 reported that chemisorption of n-octyltriethoxysilane from a dry toluene solution on a dehydrated silica amounts 0.30 fimol/m2. However, if a toluene solution containing traces of water is used, the amount of chemisorbed silane increases up to 1.25 /tmol/m2. 

If carbonylation of a trialkylborane is conducted in the presence of water, the water promotes migration of a second alkyl group from the boron centre to the carbon atom derived from carbon monoxide. Subsequent oxidation by alkaline hydrogen peroxide gives a ketone which bears two substituents derived from the trialkylborane. A pathway which accounts for this is shown in Figure B3.3. 

This effect of polyhydroxyl compounds may not be quite as simple as it has been described, as the structure of the polyhydroxyl compound may play some part in effective stabilization of enzymes in wet systems. Thus Fujita et al, (20) reported that inositol was more effective than sorbitol in stabilizing lysozyme in aqueous solutions. Both compounds contain six hydroxyl groups, but inositol is cyclic in structure whereas sorbitol is linear, Fig 10. The interaction of polyhydroxyl compounds with water promotes a change in the molecular structure of water. Inositol was reported to have a larger structure-making effect than sorbitol, which accounted for the greater stabilization effect of this compound. 

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